The present invention relates to a visual inspection method, and an apparatus, for detecting defects including minute pattern defects and particles on the basis of an image of an object, which has been acquired by use of lamp light, a laser beam, an electron beam, or the like, and for classifying the defects, the visual inspection method and apparatus being targeted for thin film devices including a semiconductor wafer, TFT, and a photo mask. In particular, the present invention relates to a visual inspection method and an apparatus that are suitable for visual inspection of a semiconductor wafer.
Thin film devices such as a semiconductor wafer, a liquid crystal display, and a magnetic head of a hard disk are manufactured through many fabrication processes. In the manufacturing of such thin film devices, with the objective of improving and stabilizing yields, visual inspection is performed for each series of processes. In the visual inspection, defects such as a pattern defect and a foreign particle are detected on the basis of an image acquired by use of lamp light, a laser beam, an electron beam, or the like. At the same time, there is also a case where defects are classified on the basis of features of defects such as the brightness and the size. For example, Japanese Patent Laid-Open No. 2002-257533 (corresponding to U.S. application Ser. No. 10/050,776) discloses an inspection apparatus that classifies defects into particles which are convex defects and scratches which are concave defects according to a difference in intensity between scattered light by vertical lighting and scattered light by oblique lighting. When defect classification conditions of the inspection apparatus having such a defect classification function are determined, it is necessary to instruct classes into which defects are classified by reviewing, and to determine the relationship between a feature and a class. In the above example, the classes into which defects are classified are a particle class and a scratch class. Accordingly, it is assumed that the intensity of scattered light at the time of vertical lighting and the intensity of scattered light at the time of oblique lighting are features. Then, on the basis of a two-dimensional scatter diagram, a discrimination line is manually set.
Incidentally, other than the technique disclosed in the Japanese Patent Laid-Open No. 2002-257533 described above, techniques which are known as the background art pertaining to the present invention include: the technique disclosed in Japanese Patent Laid-Open No. 2004-47939; the technique disclosed in Japanese Patent Laid-Open No. 2003-59984 (corresponding to U.S. Pat. No. 6,876,445 B2); the technology disclosed in Japanese Patent Laid-Open No. 2004-117229 (corresponding to U.S. application Ser. No. 10/672,010); and the technique disclosed in the 13th workshop on automation of visual inspection, pp. 99-104 (December, 2001).
As far as the visual inspection of semiconductor wafers are connected, as a result of the miniaturization of patterns, the size of a target defect to be detected becomes smaller, and the number of detected defects increases to a level ranging from several thousand to tens of thousands. Therefore, because it is practically impossible to review all defects, it is necessary to sample defects, the number of which is from several tens to several hundreds, before the sampled defects are reviewed. However, when defects are sampled at random, if a defect occurrence ratio deviates from the usual, the same kind of defects are mainly selected, resulting in the unclear relationship between a feature and a class. Accordingly, classification conditions cannot be correctly set, which was a problem to be solved.